1. Field of the Invention
The present invention relates to a photo-detecting device which records/reproduces a signal such as visual information on/from an information recording means such as an optical disk, and more particularly to a structure of a photo detector that receives a light reflected from the optical disk, and a method for processing the signal outputted therefrom.
2. Description of the Prior Art
Generally, reading operation of a signal optically recorded on an information recording means such as an optical disk is performed by a photo detector detecting the light reflected from the disk, wherein the photo detector receives the reflected light by a plurality of divided light receiving sections thereof, and obtains a reproduced signal and various servo signals by adding or subtracting the signals outputted from each of the light receiving sections.
For example, FIG. 7 shows a photo-detecting device having a photo diode which is divided into four sections as a photo detector 10, wherein the amount of reflected light RL radiated against the four vertically and horizontally divided light receiving sections Pa, Pb, Pc, Pd is totaled at an adder 11 so as to obtain an RF signal, and a difference between the amounts of light received on the mutually diagonal light receiving sections, that is {(Pa+Pc)-(Pb+Pd)}, is calculated by an adder 12, 13 and a subtracter 14 so as to obtain a focus control signal FE. By the way, an astigmatism generating means should be inserted in the course of the light beam for obtaining this focus control signal FE.
Further, as shown in FIG. 8, an analog camera element composed of a photo-diode array, a charge coupled device or the like has also been adopted as a photo detector 20. Generally, when the number of the divided light receiving elements is increased, a positioning arrangement of the photo detector, which is essential in the embodiment shown in FIG. 7; an arrangement such that the spot of the reflected light RL should be positioned so as to be located on the center of the four light receiving sections Pa, Pb, Pc, Pd, can be obviated as the case of the above photo detector 20, and still further, the amounts of the light received by the respective light receiving sections can also be read out sequentially as analog quantities.
By the way, when a reproduced signal is obtained by the above-described photo-detecting device, if the amount of the reflected light RL radiated to the photo detector is not enough, an induced noise is generated through an effect of the nearby electromagnetic field, and the thus generated noise is mixed with a light-electricity converted analog signal to deteriorate the SN ratio of the reproduced signal.